The fast f/2.8, coupled with IS. The quality of the images are sharp, but I'd have to say the 24-70 is sharper since I use both at work.

Cons:

The cheap build, dust, IS system messing up after 9 months.

As in another review, 9 months into owning it, the IS system vibrating violent. I mean violently as in non-stop when I tried to focus. The lens is as of now is being repaired. As for the dust issue, I mean honestly, when has dust completely RUINED an image for you? I pick out only a handful of images out of the hundreds I take on an average shoot anyways.